Crewman (also known as ables'man or able crewman) was an enlisted naval rate, a type of military rank used by the service organizations of different cultures. This title was the lowest enlisted rank, subordinate to a petty officer. In comparison to infantry ranking systems, this rank was approximately equivalent to the grade of private. In Klingonese, this rank was referred to as bekk.

In Starfleet, a "crewman" could refer to either a person who held the actual rank or simply any person who was assigned to an organization or starship. The grade of crewman could further be divided into several "classes", such as "crewman first class", "crewman second class", etc. (TOS: "The Man Trap")

Although this rank has never been mentioned, three grades of crewman insignia were in use during the 22nd century. This lowest grade was never mentioned by name, but the insignia was worn by Daniels, Cunningham, and others.

Although Star Trek has often been ambivalent about enlisted ranks and insignia, there have been mentions of the term "crewman" since TOS: "The Man Trap", although it is continuously impossible to tell who this rank was bestowed upon, since both crewman and ensigns (as well as chief petty officers) had no visible rank insignia.

Fletcher's original costume notes actually referred to the rank of crewman as "able seaman", a term which has been used nowhere else in Star Trek with most sources referring to the pin designed by Fletcher simply as "crewman".

By TNG: "The Drumhead", it was established in dialog that Simon Tarses was an enlisted crewman who had not gone to the Academy; he had a blank collar. This lack of rank insignia for crewmen and noncoms was used throughout Deep Space Nine and Voyager, although chief petty officers were assigned different insignia.